review feedback

Author: dg-pb

Doc/library/functools.rst

@@ -353,8 +353,8 @@ The :mod:`functools` module defines the following functions:
                                   f"got {len(fargs)}")
               newargs = list(args)
               j = 0
-              for i in range(len(args)):
-                  if args[i] is Placeholder:
+              for i, arg in enumarate(args):
+                  if arg is Placeholder:
                       newargs[i] = fargs[j]
                       j += 1
               newargs.extend(fargs[j:])
@@ -381,7 +381,7 @@ The :mod:`functools` module defines the following functions:
    If ``Placeholder`` sentinels are present in *args*, they will be filled first
    when :func:`partial` is called. This allows custom selection of positional arguments
    to be pre-filled when constructing :ref:`partial object<partial-objects>`.
-   If ``Placeholder`` sentinels are used, all of them must be filled at call time.:
+   If ``Placeholder`` sentinels are used, all of them must be filled at call time:
 
       >>> from functools import partial, Placeholder
       >>> say_to_world = partial(print, Placeholder, 'world!')

Lib/functools.py

@@ -281,18 +281,22 @@ class PlaceholderType:
     The type of the Placeholder singleton.
     Used as a placeholder for partial arguments.
     """
-    _instance = None
+    _singleton = None
+
     def __new__(cls):
-        if cls._instance is None:
-            cls._instance = object.__new__(cls)
-        return cls._instance
+        if cls._singleton is None:
+            cls._singleton = object.__new__(cls)
+        return cls._singleton
 
     def __repr__(self):
         return 'Placeholder'
 
     def __bool__(self):
         raise TypeError("Placeholder should not be used in a boolean context")
 
+    def __reduce__(self):
+        return type(self), ()
+
 
 Placeholder = PlaceholderType()
 
@@ -406,7 +410,7 @@ def __setstate__(self, state):
         self.placeholder_count = placeholder_count
 
 try:
-    from _functools import partial, Placeholder
+    from _functools import partial, PlaceholderType, Placeholder
 except ImportError:
     pass
 

Lib/test/test_functools.py

@@ -247,6 +247,13 @@ def test_placeholders_optimization(self):
         expected = (-1, 0, 1, 2, 3, 4, 5)
         self.assertTrue(expected == got and empty == {})
 
+    def test_construct_placeholder_singleton(self):
+        PH = self.module.Placeholder
+        tp = type(PH)
+        self.assertIs(tp(), PH)
+        self.assertRaises(TypeError, tp, 1, 2)
+        self.assertRaises(TypeError, tp, a=1, b=2)
+
     def test_repr(self):
         args = (object(), object())
         args_repr = ', '.join(repr(a) for a in args)

Modules/_functoolsmodule.c

@@ -74,8 +74,8 @@ static void
 placeholder_dealloc(PyObject* placeholder)
 {
     /* This should never get called, but we also don't want to SEGV if
-     * we accidentally decref None out of existence. Instead,
-     * since None is an immortal object, re-set the reference count.
+     * we accidentally decref Placeholder out of existence. Instead,
+     * since Placeholder is an immortal object, re-set the reference count.
      */
     _Py_SetImmortal(placeholder);
 }
@@ -114,7 +114,7 @@ static PyType_Slot placeholder_type_slots[] = {
 };
 
 static PyType_Spec placeholder_type_spec = {
-    .name = "partial.PlaceholderType",
+    .name = "functools.PlaceholderType",
     .basicsize = sizeof(placeholderobject),
     .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_IMMUTABLETYPE,
     .slots = placeholder_type_slots
@@ -1701,9 +1701,6 @@ _functools_exec(PyObject *module)
         return -1;
     }
 
-    // if (PyModule_AddObject(module, "Placeholder", Py_GetPlaceholder()) < 0) {
-    //     return -1;
-    // }
     state->placeholder_type = (PyTypeObject *)PyType_FromModuleAndSpec(module,
         &placeholder_type_spec, NULL);
     if (state->placeholder_type == NULL) {